Journal
COMBUSTION THEORY AND MODELLING
Volume 20, Issue 4, Pages 632-657Publisher
TAYLOR & FRANCIS LTD
DOI: 10.1080/13647830.2016.1164344
Keywords
Lewis numbers; transport properties; laminar flames; turbulent flames; computational cost
Categories
Funding
- Department of Defense, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship [32 CFR 168a]
- US Department of Energy - Basic Energy Sciences [DE-SC006591]
- Air Force Office of Scientific Research [FA9550-12-1-0472, FA9550-12-1-0144]
- Office of Science of the U. Department of Energy [DE-SC006591]
- National Science Foundation [CTS-130006]
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Accurate computation of molecular diffusion coefficients in chemically reacting flows can be an expensive procedure, and the use of constant non-unity Lewis numbers has been adopted often as a cheaper alternative. The goal of the current work is to explore the validity and the limitations of the constant non-unity Lewis number approach in the description of molecular mixing in laminar and turbulent flames. To carry out this analysis, three test cases have been selected, including a lean, highly unstable, premixed hydrogen/air flame, a lean turbulent premixed n-heptane/air flame, and a laminar ethylene/air coflow diffusion flame. For the hydrogen flame, both a laminar and a turbulent configuration have been considered. The three flames are characterised by Lewis numbers which are less than unity, greater than unity, and close to unity, respectively. For each flame, mixture-averaged transport simulations are carried out and used as reference data. The current analysis suggests that, for numerous combustion configurations, the constant non-unity Lewis number approximation leads to small errors when the set of Lewis numbers is chosen properly. For the selected test cases and our numerical framework, the reduction of computational cost is found to be minimal.
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